Colloidal Solution Of Nanoparticles Research Articles

Plant mediated greener approach for synthesis of silver nanoparticles from <i>Digitalis purpurea</i> plant and its antibacterial activity

In this paper, silver nanoparticles were biosynthesised using aqueous Digitalis purpurea leaf extract. The biosynthesised silver nanoparticles were characterised by UV-visible (UV-vis) spectrophotometer, Fourier transform infrared spectroscopy (FTIR), x-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), energy dispersive x-ray (EDX) analysis and high-resolution transmission electron microscopy (HRTEM). In the colloidal solution, the formation and stability of the silver nanoparticles were identified by UV-visible and it showed the maximum absorption at 452 nm. XRD and HRTEM analysis showed that the silver nanoparticles were cubic structured, face centred with a particle size of 25 nm and EDX evidenced the presence of silver element. The FTIR analysis revealed the existence of various functional groups. Antibacterial activity of the synthesised silver nanoparticles was evaluated against the gram-negative Escherichia coli (MTCC 1652) and gram-positive Staphylococcus aureus (MTCC 316) bacteria, showed the efficient activity against both the gram-negative and gram-positive microorganisms.

Antimicrobial Activity of Differently Concentrated Nanoparticle Dispersions

Preparation of nontoxic antimicrobial solutions is a priority in the development of new antibiotics. The in vitro effect of the chemical composition of the dispersed phase and dissolved solids in the dispersion medium on the antimicrobial properties of aqueous colloidal solutions of nanoparticles of a number of metals and metal oxides against microorganisms of different species - bacterial dental plaque, Bacillus cereus, and spores of vaccine strain Bacillus anthracis STI - 1 were studied in this work.

The Review of Small Size Silver Nanoparticle Neurotoxicity: A Repeat Study

Repeated oral gavages silver nanoparticle colloidal solution ingestion procedures for AgNps neural toxicity have been investigated in Swiss albino mouse fetuses’ brain at the ultra-structural (TEM) level by transmission electron microscopy and Nikon bright field microscopy. Transmission electron microscopy probe identified neural toxicity in the brain of mice fetuses in the form of mitochondrial autophagy, dysmorphology & dysfunction of cellular organelles vacuolization of neuronal cell, blood brain barrier inflammation, astrocytic swelling, Gliosis and a well visualized differentiation to the reaction products. Multiple reaction product localization was visible in the form of smaller size silver nano particles (1 to 20 nm range) percolation and perimembranous multiple patchy condensations focuses appeared from inside and outside of neuronal cell membrane. Histologically cell and tissue dysmorphology was observed in the form of unipolar brush cell and lugaro cells degeneration with dysmorphology of corticomedullary layers of cerebrum, cerebellum and hippocampus. In twice, lower dose (0.5 and 1 mg/kg b.w./ day) and higher dose (10 and 15 mg/kg b.w./day) small size silver nano particles were found adhered both side of cell membrane, mitochondria and endocytotic vesicle. Neural histochemistry of fetal cortex by Golgi staining procedure showed reduction number of dendrite arborisation and unipolar neuron with basket cells degeneration and dysmorphology. But the intensity of such was found almost low or equal to control in lower dose and high in higher dose and concentration. Small size silver nano particles exhibits more neurotoxic effect comparatively to other metal nanoparticles because of easy penetration and disintegrity to BBB.

Impact of Silver Nanoparticle Suspensions on Mixtures of Fungal and Bacterial Microorganisms of Food Production

Providing of food safety is a fundamental problem of food production. Silver nanoparticles demonstrate antimicrobial action against multiple bacterial species while not affecting fungal species. Nanosilver colloidal solutions stabilized with Gum Arabic and glycine with the size of nanoparticles from 7 to 12 nm were tested. The experiments were conducted upon cultivating some common fungal microorganisms implemented in food production, such as Aspergillus oryzae and Saccharomyces cerevisiae on different media contaminated with bacteria Escherichia coli, Erwinia herbicola, Pseudomonas fluorescens, Bacillus cereus, and Pediococcus claussenii. Samples were treated with silver nanoparticles colloidal solutions of various concentrations. The results show that nanoparticles inhibit the growth of bacteria within the concentration of 0.03-0.05 g/dm3 in solid media and 0.001-0.005 g/dm3 in liquid media. The specified inhibitory concentrations did not affect the growth of fungi.

Plasmonics-Based Detection of Virus Using Sialic Acid Functionalized Gold Nanoparticles.

Biosensor for the detection of virus was developed by utilizing plasmonic peak shift phenomenon of the gold nanoparticles and viral infection mechanism of hemagglutinin on virus and sialic acid on animal cells. The plasmonic peak of the colloidal gold nanoparticles changes with the aggregation of the particles due to the plasmonic interaction between nearby particles and the color of the colloidal nanoparticle solution changes from wine red to purple. Sialic acid reduced and stabilized colloidal gold nanoparticle aggregation is induced by the addition of viral particles in the solution due to the hemagglutinin-sialic acid interaction. In this work, sialic acid reduced and stabilized gold nanoparticles (d = 20.1 ± 1.8 nm) were synthesized by a simple one-pot, green method without chemically modifying sialic acid. The gold nanoparticles showed target-specific aggregation with viral particles via hemagglutinin-sialic acid binding. A linear correlation was observed between the change in optical density and dilution of chemically inactivated influenza B virus species. The detection limit of the virus dilution (hemagglutinination assay titer, 512) was shown to be 0.156 vol% and the upper limit of the linearity can be extended with the use of more sialic acid-gold nanoparticles.

Formation of platinum nanoparticle colloidal solution by gamma-ray irradiation

ABSTRACTPlatinum nanoparticle colloidal solution with a small amount of impurities was formed from a suspension of hexahydroxy platinic acid (SHHPA) by gamma-ray irradiation to suppress changes in water chemistry such as electrical conductivity and concentration of impurities in the reactor water during noble metal chemical addition in plant operation. The SHHPA was prepared from sodium hexahydroxyplatinate solution by using an H-type cation exchange resin. Optimum conditions for formation of the platinum nanoparticle colloidal solution were the following: absorbed dose of gamma-ray irradiation, >6 kGy; pH of solution, >8.2; air saturation; no methanol addition. Characteristics of the formed platinum nanoparticles were as follows: mean particle size, 2.3 ± 0.5 nm; particle charge, negative; isoelectric point at a pH of 3.5 ± 0.1; the chemical compound consisted mainly of platinum dioxide without platinum metal. No precipitation of platinum nanoparticles was observed after storage time of 1 year without any stirring in a room where the temperature varied from about 10 to about 35 °C.

Removal of mixture of ZnO and CuO nanoparticles (NPs) from water using activated carbon in batch kinetic studies.

The aim of this study was to understand the effects of pH (5, 6, 7, 8, 9) and activated carbon (AC) concentration (0.01, 0.1, 1, 10, 100 g/L) on the removal of a colloidal solution of nanoparticles (NPs) (ZnO + CuO) using AC in batch kinetic studies. Results revealed that adsorption capacities of AC for Zn and Cu (individually) were 0.9 ± 0.028 mg/g (91.3% removal) and 0.95 ± 0.036 mg/g (95.6% removal) in deionized water and 0.6 ± 0.038 mg/g (78% removal) and 0.75 ± 0.078 mg/g (83% removal) in wastewater at pH 8 (Zn) and pH 6 (Cu) respectively. In a colloidal solution mixture of zinc oxide nanoparticles (ZnONPs) and copper oxide nanoparticles (CuONPs), adsorption capacity of AC for Zn in deionized water was 0.71 ± 0.051 mg/g (74.7% removal) and in wastewater was 0.576 ± 0.019 mg/g (69% removal) and for Cu in deionized water was 0.82 ± 0.017 mg/g (81.2% removal) and in wastewater was 0.6 ± 0.032 mg/g (71.5% removal). Overall, this study provided a detailed analysis of the removal capacity of AC and indicated that AC can be used as an efficient adsorbent filter for removing engineered NPs like ZnONPs and CuONPs (single and mixture) from water. As there is a need for removing NPs from wastewater, removal of NPs using an AC-based adsorptive-filter might become a promising method.

Palladium/γ-Fe2O3 nanoparticle mixtures for acetone and NO2 gas sensors

The functionalization of Fe3O4/γ-Fe2O3 nanoparticles (NPs) gas sensors with Pd NPs was studied. NPs films were deposited from the mixtures of Fe3O4/γ-Fe2O3 and Pd NPs colloidal solutions by modified Langmuir-Schaefer technique onto Al2O3 substrates, the NP size being 6–7nm. Samples were composed from 4 Fe3O4/γ-Fe2O3 NP monolayers (MLs), either pure or doped by Pd at the different NPs Pd: Fe3O4/γ-Fe2O3 proportions. NPs and films were studied by DLS, GI XRD, SEM and EDS. Sensors were tested toward acetone vapors and NO2 at concentration range of 5–200ppm and 0.5–12ppm respectively in dry air and under working temperatures range 200–500°C. Before testing 1nm, surfactant capping was removed by UV irradiation. Pd-doped Fe3O4/γ-Fe2O3 sensors showed p-type gas response, higher conductance and higher conduction activation energies compared to pure Fe3O4/γ-Fe2O3 sensor that gives n-type gas response. Results are explained in terms of surface interactions with oxidizing and reducing species, and electrical conduction mechanisms.

Controlled preparation and visible light photocatalytic activities of corn cob-like Au–ZnO nanorods

A facile method to prepare well-shaped nanohybrids of Au–ZnO nanorods (NRs) has been demonstrated, which is through polyvinylpyrrolidone-assisted in situ nucleation and growth of ZnONRs in the colloidal solution of Au nanoparticles (NPs). The obtained Au–ZnONRs shows uniform corn cob-like morphology with AuNPs evenly deposited on the surface of hexagonal ZnONRs and can be dispersed in aqueous solution to achieve photodegradation of organics. Moreover, the loading amount of AuNPs can be tuned to optimize the photocatalytic performance. The nanohybrid of Au–ZnONRs with optimized AuNP loading exhibits superior photocatalytic activity than ZnONRs alone, demonstrating ~90% Rhodamine B degradation within 18 h under the visible light of 420–780 nm, a wavelength range that does not overlap with ZnO absorption. The observed performance improvement is likely due to the coupling effect between ZnONRs and AuNPs, which functionalizes ZnONRs with visible light utilization and enhances charge separation. The strategy presented here not only provides a new approach for the controlled modification of 1D semiconductor nanostructures, but also holds good potential for applications such as degradation of organic pollutants.

Facile synthesis of water‐dispersible magnetite nanorings from surfactant‐free hematite nanorings

Surfactant-free α-Fe2O3 nanorings (NRs) were directly converted into water-dispersible Fe3O4 NRs through a simple and straightforward approach. In this process, uniform α-Fe2O3 NRs obtained through hydrothermal synthesis method are firstly thermally reduced to hydrophobic Fe3O4 NRs in the presence of hydrophobic oleic acid surfactant and non-polar trioctylamine solvent (under a flow of 5% H2/95% Ar). Subsequently, oxidative cleavage of oleic acid capping agent using sodium periodate oxidising agent is imparted to yield water-dispersible Fe3O4 NRs. As compared with the traditional solid-state reduction in tube furnace, the obtained Fe3O4 NRs using solution-based reduction process can retain its original uniform ring shape with good crystallinity and well-defined magnetic vortex domain. Moreover, with the presence of azelaic acid on the surface of hydrophilic Fe3O4 NRs, antibody or drugs can be easily conjugated, which further boost its potential theranostics application. This work provides a convenient approach to convert surfactant-free nanoparticle (NP) powders into water-dispersible NPs colloidal solutions for various biomedical applications.

Removal of Metal Nanoparticles Colloidal Solutions by Water Plants.

The ability of seven species of aquatic plants (Elodea canadensis, Najas guadelupensis, Vallisneria spiralis L., Riccia fluitans L., Limnobium laevigatum, Pistia stratiotes L., and Salvinia natans L.) to absorb metal nanoparticles from colloidal solutions was studied. It was established that investigated aquatic plants have a high capacity for removal of metal nanoparticles from aqueous solution (30–100%) which indicates their high phytoremediation potential. Analysis of the water samples content for elements including the mixture of colloidal solutions of metal nanoparticles (Mn, Cu, Zn, Ag + Ag2O) before and after exposure to plants showed no significant differences when using submerged or free-floating hydrophytes so-called pleuston. However, it was found that the presence of submerged hydrophytes in aqueous medium (E. canadensis, N. guadelupensis, V. spiralis L., and R. fluitans L.) and significant changes in the content of photosynthetic pigments, unlike free-floating hydrophytes (L. laevigatum, P. stratiotes L., S. natans L.), had occur. Pleuston possesses higher potential for phytoremediation of contaminated water basins polluted by metal nanoparticles. In terms of removal of nanoparticles among studied free-floating hydrophytes, P. stratiotes L. and S. natans L. deserve on special attention.

Fully inkjet-printing of metal-polymer-metal multilayer on a flexible liquid crystal polymer substrate

This study investigated a fully inkjet-printed metal/polymer/metal multilayer on a liquid crystal polymer substrate by using two alternately printed inks. A silver nanoparticle colloidal solution ink was used for the metal layers, and a dielectric-based SU-8 ink was used for the polymer layer. The conditions influencing the inkjet-printed polymer layer, including the surface treatment, drop spacing, and thermal treatment, were established; notably, surface wetting of the preceding layer, including various materials in the same level, affected the subsequent inkjet-printed layer. Thus, the conditions of thermal treatment should be carefully controlled to ensure an appropriately wet surface for printing. An inkjet-printed metal/polymer/metal multilayer was then fabricated using the determined printing parameters, and the results demonstrated the integrity of fully inkjet-printed technology. This success creates new feasible opportunities for electronic printing applications.

Optimization of physicochemical conditions to produce silver nanoparticles and estimation of the biological effects of colloids synthesized

The results of our study of the size, optical properties, and aggregate stability of silver nanoparticles in aqueous solutions 1, 2, and 12 months after their synthesis are reported. It has been shown that nanoparticles synthesized using a combined application of physical factors, such as ultraviolet radiation, ultrasound, and uniform mixing (providing conditions of isolation from the atmospheric air) are smaller in size (from 1 to 10 nm) and have more homogenous distribution of the diameter of nanoparticles. A lower aggregation has been noted compared with particles prepared without observing the synthesis algorithm that was developed and conditions given above. The results of studying antimicrobial antiseptic properties based on a colloidal nanosilver solution prepared using the technology of diffusion-cavitation photochemical reduction of silver nitrate are also reported. A high antimicrobial activity of the resulting colloidal solution with silver nanoparticles against clinical isolates of P. aeruginosa, A. baumanii, and E. coli has been demonstrated as compared with the original silver nitrate and the ligand (polyvinylpyrrolidone) used in the synthesis of the colloid at the same concentration. At a concentration of 10 μg/mL, a colloidal solution with silver nanoparticles has been found to possess bactericidal activity against two isolates of P. aeruginosa, three isolates of A. baumanii, and five isolates of E. coli. At a concentration of 1 μg/mL, the colloidal solution of silver nanoparticles has possessed only bacteriostatic activity against all isolates of the bacteria. The minimum bacteriostatic inhibitory concentration of nanosilver has determined to be 3 μg/mL.

Structural and luminescence properties of silicon nanocrystals in colloidal solutions for bio applications

Luminescent silicon nanoparticles are promising not only for optoelectronics or photovoltaics, but also for biological and medical research, e.g., as luminescent markers, for drug delivery, or toxicity studies. For intracellular biological research, it is necessary to prepare water-based or isotonic colloidal solutions of nanoparticles which are stable and non-toxic. In this work, we compare structural and optical properties of silicon nanocrystals in colloidal solutions, obtained by two fundamentally different methods: A microplasma-based synthesis (a “bottom-up” technique) and porous silicon prepared by electrochemical etching of a silicon wafer (a “top–down” method). Low-pressure microwave plasma synthesis produces ∼5–8 nm large silicon nanocrystals while the porous siliconcontains clusters ∼60–70 nm in diameter, composed of nanometer-sized luminescent nanocrystals. However, both types of nanoparticles are prone to agglomeration, as was confirmed by dynamic light scattering and zeta potential measurements. We have attempted to stabilize the nanoparticles via modification of the their surface by methyl groups; however, the mechano-photo-chemical treatment procedure leading to coverage with methyl groups is less efficient in the case of plasma-synthesized nanoparticles than in porous silicon. The first attempt of steric stabilization of the colloidal solutions of the silicon nanoparticles was succesfully carried out too; good candidates for stabilization are bovine serum albumin and glycine.

Encapsulation of anticancer drug copper bis(8-hydroxyquinoline) in hydroxyapatite for pH-sensitive targeted delivery and slow release

There is a conspicuous progress in increasing anticancer drug delivery through the utilization of nanoparticles (NPs) as drug delivery agents. Hydroxyapatite (HA) gives improved clinical effectiveness of drugs by reducing systemic toxicity and broadening the spectrum of drug delivery since it is biocompatible and it can be targeted towards tumor cells. Herein, investigation of the potential of enhancing controlled drug release of the template model drug, copper bis-(8-hydroxyquinoline), by encapsulating it in hollow hydroxyapatite nano-carriers, is presented. Hydroxyapatite nanoparticles are synthesized by following four different routes to optimize its efficacy of drug loading. Copper bis-(8-hydroxyquinoline) is encapsulated by Method (a) which was effected by stirring the model drug and porous HA NPs in colloidal solution and Method (b) which was done during synthesis of hydroxyapatite nanoparticles in a solution of the model drug. In synthesizing nanoporous HA NPs, calcium carbonate is used as a template to create voids in HA. In each method, Ca/P ratio was ensured to be kept at 1.67:1. Appealing results are reported for the encapsulated product which was prepared by Method (a2). Method (a) was done at three different molar ratios of PO43−:CO32– and best result was obtained for that utilized 2.003:1 molar ratio (Method (a2).). It produced 98.67% of encapsulation efficiency and 2.9522mg/g of drug loading capacity. Release kinetics was studied at a range of pH values; the lower the pH of the medium the higher is the drug release. For instance, when considering the product which exhibited high encapsulation efficiency and high drug loading capacity, at pH3.5 during the first 8h it elicited about 13% of release, at pH5.0 about 8% release while at pH6.0 it was just 2.5%. During the 24-hour span, pH3.5 exhibited about 23.8%, at pH5.0 approximately 9% with an increasing trend of release and at pH6.0 showed a value just above 2.5%. As such, acidity of the cancerous cells can be made use to increase the drug slow-release kinetics at the vicinity of the cancer cells.

Metal–metal bonding process using cuprous oxide nanoparticles

This work performs metal–metal bonding by using cuprous oxide (Cu2O) nanoparticles prepared by reduction in aqueous solution. A colloid solution of Cu2O nanoparticles was prepared by mixing Cu(NO3)2 aqueous solution and NaBH4 aqueous solution. Cu2O nanoparticles with a size of 111±34nm, cubic crystal phase, and crystal size of 21.2nm were produced at initial concentrations of 0.010M Cu(NO3)2 and 0.010M NaBH4 at a temperature of 40°C. The Cu2O particles contained not only CuO bonds but also Cu0Cu0 bonds, which indicated formation of fine cluster-like domains composed of Cu0Cu0 bonds. The shear strength required for separating the metallic Cu discs bonded by using the particles as a filler at 400°C in H2 gas was as high as 27.9MPa, which was comparable to the shear strengths of metallic Cu particles and CuO particles reported in our previous works. Metallic Cu single crystallites were produced during the bonding process. The presence of the fine cluster-like domains promoted epitaxial particle growth of the metallic Cu and formation of the micron-sized domains composed of nano-sized and submicron-sized single crystals, which provided the strong bonding.

(Invited) Single Molecule SERS with Directionally Arrayed Gold Nanoparticle Dimers on Substrate

This study achieved single molecule detection, for the first time, on the prefabricated substrate for SERS (surface enhanced Raman spectroscopy) with non-resonant molecules. The substrate with directionally arrayed gold nanoparticle dimers enables huge Raman enhancement and is expected for single molecule identification and structural analysis of a wide range of bio/chemical molecules. Due to remarkable capabilities of rapid and highly-sensitive structural analysis and identification of bio/chemical molecules, SERS is expected as a powerful tool for single molecule analysis. Conventionally molecularly bridged metal nanoparticle aggregates has been used for single molecule SERS so far. In these demonstrations, the aggregates are generated mixing nanoparticle colloid and target analyte solutions with hour-level long incubation time. Rhodamine 6G or crystal violet, which offers a resonant Raman effect, has been used. Therefore, for example, this technique cannot be applied to in-situ real-time analysis of various bio/chemical molecules such as hazardous substances, cell products and nucleobases in microfluidic devices. Although prefabricated SERS structures such as particle aggregates on a substrate are appropriate for the above application, no demonstration of single molecule SERS has been reported. It is because the reported SERS substrate has an insufficient Raman enhancementfactor for single molecule SERS. In this study, for the first time, we demonstrate single molecule SERS of non-resonant molecules using the prefabricated substrate. In order to improve Raman enhancement factor of SERS substrates, this study uses the nano-engineered SERS substrate on which particle dimers are directionally arrayed to match all dimers axes to a polarization direction of incident light. This arrangement is expected to enable single-molecule SERS analysis, because of the large Raman enhancement achieved by coupling with the polarization direction. Arraying the dimers directionally, the huge enhancement can be achieved at all dimers. The substrate was fabricated using nanotrench-guided self-assembly. At the beginning of this fabrication, a colloidal particle solution was injected between a cover glass and a template substrate of Si with nanotrench template. On drying the aqueous particle dispersion between the substrates, the water surface line moved backward and the particles became concentrated near the edge of the meniscus. The drag force pressed the particles onto the template substrate. When the meniscus passed over the templates, particles were trapped on the template. Gold nanoparticles with mean diameters of 100 nm were used in this study. 4,4'-Bipyridine molecule, which is non-Raman resonance molecule and a pesticide material, was used for demonstrating single molecule detection. We performed around 50 Raman measurements for each measurement time (1 s or 0.05 s) and molecule concentration (10−5 or 10−11 M). 10−11 M corresponds to one molecule per volume of a cube with a side 5.5 µm. The statistical analysis was performed. All spectra were discriminated based on with or without a peak at around 1609 cm−1, which is one of the Raman shifts derived from the target molecule. At 10−5 M concentration, all spectra exhibited clear peaks. The distribution of Raman intensities were fitted by one Gaussian curve. At 10−11 M concentration, the experimental data at 1 s and 0.05 s were fitted by three and two Gaussian curves, respectively. These are consistent with a Poisson distribution. The change in the statistical distribution from Gaussian (10−5 M) to Poisson (10−11 M) with decreasing the concentration reflects the probability of detecting 0 (background noise), 1, 2 molecule(s) at 1 s. Two Gaussian curves indicate 0 and 1 molecule at 0.05 s. Average relative intensities of 0, 1 and 2 molecule(s) were 0.89, 1.06, and 1.28 at 1 s, respectively. The net relative intensities of 2 molecules are calculated to 1.28−0.89=0.39, which is 1.8 times as much as 1 molecule, 1.28−1.06=0.22. From these experimental data and statistical analysis, we confirmed that the developed substrates achieved single molecule SERS detection. Finally, nucleobases identification with single molecule sensitivity was demonstrated using 10−11 M solutions of adenine and cytosine. The obtained peaks were enough clear to identify the nucleobases. Therefore, a wide range of bio/chemical molecules is expected to be structurally analyzed and identified by single molecule SERS on the prefabricated substrate.

Effects of Systemic Introductions of Nanoparticles and Salts of Gold and Silver on the Size of the Nuclei of Hypothalamic Neurons in Male Rats

We studied the effects of course (10 days) intraperitoneal injections of salts of gold and silver and colloid solutions of nanoparticles of these metals on the size (mean value of the cross-sections) of the nuclei of hypothalamic neurocytes localized in the preoptic and arcuate nuclei of immature male albino rats. In animals injected with a solution containing tetrachloroaurate ions, the examined morphometric parameters in both structures significantly exceeded the control values. Injections of gold nanoparticles led to significant decreases in the cross-sections of the neurocyte nuclei; thus, the pattern of the effects of gold depended on its physicochemical form. Injections of both silver salt (AgNO3) and silver nanoparticles led to drops in the mean values of cross-sections of the nuclei of neurocytes. Therefore, shifts of the studied morphofunctional characteristics of the cells belonging to the hypothalamic nuclei resulting from systemic injections of colloid solutions (nanoparticles) of gold and silver are indicative of suppression of functions of the central link of the hypothalamo-hypophyseal-gonadal system after the influence of these factors.

Investigation of the aluminum phthalocyanine nanoparticles colloidal solutions pH-dependent photoluminescence kinetics in pico- and nanosecond time range

In this study, the fluorescence intensity decay of aluminum phthalocyanine nanoparticles colloidal solutions at different pH was investigated. Hamamatsu Streak-Camera (C10627 - 13 Hamamatsu Photonics) with picosecond temporal resolution (15 ps) was used to carry out the measurements. For excitation we used Hamamatsu Picosecond Light Pulser PLP - 10 with 637 nm wavelength and 65 ps pulse duration. The changes in fluorescence decay kinetics were found during the experiment. The number of fluorescence lifetime components and duration of lifetimes depends on pH. At pH 2 the presence of two fluorescence lifetimes was recorded: the first one was 5 ns, which corresponded to the molecular form in solution, and 1.5 ns, which corresponded to bound state of phthalocyanine molecules. This work is a preparatory step towards a model which describes the interaction of aluminum phthalocyanine nanoparticles with environment in biological tissue.

Modeling of nanoparticle agglomeration and powder bed formation in microscale selective laser sintering systems

Additive manufacturing (AM) has received a great deal of attention for the ability to produce three dimensional parts via laser heating. One recently proposed method of making microscale AM parts is through microscale selective laser sintering (μ-SLS) where nanoparticles replace the traditional powders used in standard SLS processes. However, there are many challenges to understanding the physics of the process at nanoscale as well as with conducting experiments at that scale; hence, modeling and computational simulations are vital to understand the sintering process physics. At the sub-micron (μm) level, the interaction between nanoparticles under high power laser heating raises additional near-field thermal issues such as thermal diffusivity, effective absorptivity, and extinction coefficients compared to larger scales. Thus, nanoparticle's distribution behavior and characteristic properties are very important to understanding the thermal analysis of nanoparticles in a μ-SLS process. This paper presents a discrete element modeling (DEM) study of how copper nanoparticles of given particle size distribution pack together in a μ-SLS powder bed. Initially, nanoparticles are distributed randomly into the bed domain with a random initial velocity vector and set boundary conditions. The particles are then allowed to move in discrete time steps until they reach a final steady state position, which creates the particle packing within the powder bed. The particles are subject to both gravitational and cohesive forces since cohesive forces become important at the nanoscale. A set of simulations was performed for different cases under both Gaussian and log-normal particle size distributions with different standard deviations. The results show that the cohesive interactions between nanoparticles has a great effect on both the size of the agglomerates and how densely the nanoparticles pack together within the agglomerates. In addition, this paper suggests a potential method to overcome the agglomeration effects in μ-SLS powder beds through the use of colloidal nanoparticle solutions that minimize the cohesive interactions between individual nanoparticles.